Radiant heat responsive device



Dec. 7, 1943. s. G. ISSERSTEDT 2,336,399

RADIANT HEAT RESPONSIVE DEVICE Filed Dec. 22, 1941 I IIIIIIIIIIAWIII INVENTOR; wgf ia d. Issarsieilh flfforneg Patented Dec. 7, .1943

UNITED STATES. PATENT OFFICE RADIANT HEAT RESPONSIVE DEVICE Siegfried G. Isserstcdt, Minneapolis, Minn., as-

signor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application December 22, 1941, Serial No. 423,989 19 Claims. (Cl. 200-140) This invention relates generally to heat sensitive devices and is directed more specifically to devices which are responsive to changes in radiant heat.

The main purpose of the invention is to design a device which will respond to the presence or absence of combustion in a gas or oil burner furnace, but it will be obvious that the device will have many difierent applications and uses.

Another important object of this invention is to design a radiant heat responsive device which is responsive to a rate of change of the amount of radiant heat striking the device. That is, it is intended that this device shall not be calibrated but will respond to an increase or a decrease in the amount of radiant heat.

A further object of the invention is to provide a chamber which may be filled with some suitable gas which is expansible in response to heat increase, such as air, hydrogen, nitrogen, etc., to provide a pressure responsive device for responding to the pressure in said chamber, and also to provide a small leak port for slowly equalizing the pressures across said pressure responsive means after the pressure in one of the chambers has been changed due to an increase or decrease in the amount of radiant heat striking the device.

An additional object is to mount a heat absorbing member in the chamber for the purpose of absorbing radiant heat passing through the wall of the chamber, and so mounting this member that the air or other gas within the chamber may freely circulate around it so that it can be quickly heated by convection. It is also an object of this invention to round the sides of the chamher in order to facilitate the flow of these convection currents. In the preferred form of the de-v vice this chamber is ellipsoidal in shape.

Another object of the invention'is to provide a switching mechanism to be actuated by the pressure responsive means. Where this device is to be used as a combustion responsive device in combination with an automatic oil burner control system, it is desired to so construct the device that if there is any tendency for it to fail it will fail in a safe position, that is in cold position with the oil burner motor deenergized. For this reason, it is desired to bias the switching mechanism to its oil or cold position so that it will be harder for the pressure responsive means to actuate theswitching mechanism to its on or hot position than it is to operate it to its cold position. Therefore the switching mechanism is mounted at a slightly higher elevation-than the pressure responsive means and the connecting means between the pressure responsive means and the switching mechanism is mounted at an angle so that the effect of gravity on the moving parts will almost, but not quite, overcome the effect of the switch actuator mechanism and any other resistance there may be tending to prevent movement of the switch to its cold position. With theswitching mechanism so mounted, it will be seen that only a slight effort need be exertedby the pressure responsive means in order to move the switch mechanism to its cold position, whereas a much larger effort is necessary to move it to its hot position.

A still further object of the invention is to fill the heat responsive chamber with a gas which has a lower specific heat than air, such as hydrogen or nitrogen, such gas of low specific heat being capable of heating up and hence expanding more rapidly than air. This obviously makes the device even more sensitive to variations in radiant heat.

Still another object is to provide the device with a magnetic type snap action switch in which f an armature is pivoted adjacent the poles of a horse shoe magnet so that the magnet can hold the armature in either of two positions of operation.

These and other objects will readily become apparent to those skilled in the art as the following specification is read in the light of the accompanying drawing, in which: a

Figure 1 illustrates a longitudinal section of a device embodying certain features of my invention, I

Figure 2 is a section taken along the lines 2-2 of Figure 1 and looking in the direction of the arrows,

Figure 3 is a front elevation of a second form of my invention,

Figure 4 is a section taken along the line 4-4 of Figure 3 and looking in the direction of the arrows, and

Figure 5 is a longitudinal section of a third form of my invention.

Referring now to the embodiment of the invention disclosed in Figures 1 and 2 of the drawing, a housing It! is formed by a pair of cups H and 12. A partition I3 separating the two cups forms a pair of chambers within the housing indicated at H and Hi. It is desired that radiant heat be permitted to pass free y through the face of the cup I I and therefore tiliS cup must be made out of some material which will transmit -radiant heat; such as a plastic material either colored or transparent. In this instance, the cup II has been formed of glass and for the sake of convenience the partition I3 and the other cup I2 are also made of glass, although any other suitable material could be used. These members are mounted as shown in the drawing and are sealed in order to form an air-tight chamber; A member I6 is mounted in the chamber I4 for the purpose of absorbing radiant heat passing through the wall II to heat the ga within the chamber. This member is actually a very thin sheet of metal foil which is cemented or otherwise fastened to a plurality of protrusions II on th inner surface of the cup II. In order that this form may-more readily absorb radiant heat,

v the side which faces the closed end of the cup I I is suitably blackened. This sheet of foil is actually circular in shape and has a diameter slightly less than the internal diameter of the cup II so that the gas within the chamber I4 may circulate freely about the foil and therefore heat more rapidly.

A pair of tubes I9 are inserted through the walls of the cups II and I2 in order that the two chambers I4 and I5 may be pumped to remove the air therein and then filled with some v uitable gas having a low specific heat. This gas is preferably either hydrogen or nitrogen. After the chambers have been filled with this gas the tubes I9 are sealed off, as shown.

The partition I3 carries a U-shaped tube having a first open end 2| which opens into' the chamber I4, and a second open end 22 which is bent at right angles with respect to the rest'of the tube and is inserted through an opening 23 in the partition I3 and opens into the chamber I5. The. U tube 20 carries a body. of mercury 24 which occupiesthe position shown in the drawing When the pressures in the two chambers I4 and I5 are equal. A pair of filters 25 and 25 are located adjacent the open ends of the tube in orderto prevent th mercury from passing out of the tube, but which are sufiiciently porous to permit the free passage of gas therethrough.

It is desired that the mercury actuate some sort of switching mechanism and for the sake of illustration three electrodes 21, 28 and 29 have beenshown as being inserted through the tube to contact with the mercury. The electrode 21 is shown as inserted through the bottom ofthe tube and is therefore continuously in contact with the mercury. The electrode 28 is shown as inserted just below the normal level of the mercury, whereas the electrode 29 has been shown just above the normal level of the mercury.

Suitable conductors 30, 3| and 32 may be provided for connecting the electrodes 21, 28 and 29 with an external circuit. These conductors are shown as extending through the cup [2 and through the partition I3. It will be obvious that these conductors should be-made of some material which may be properly sealed to the cup I I and the partition I3 so as to make these connections air-tight. A restricted opening 33 is provided in the partition I3 for the purpose of slowly equalizing the pressures in the chambers I4 and I5 following an expansion or contraction of gas in the chamber I4. i

It will be obvious that when there is no radiant heat passing through the wall II of the housing ID that the gas in the chambers I4 and I5 will be at substantially the same temperature and the pressures in these two chambers will be equal, due to the restricted opening 33. If the housing III is so positioned that the cup II faces a burner ber I4 than in the chamber I5.

such as an oil burner, the establishment of combustion at the burner will cause a relatively large amount of radiant heat to pass through the cup II and into the chamber I4 where it will be absorbed by the blackened metal foil IS. The foil I6 will thereupon rapidlyheat the gas in the chamber I4 and cause it to expand thereby increasing the pressure in the chamber I4. This increase in pressure in chamber I4 will cause the mercury to move down in leg 34 and up in leg 35 of the U tube and therefore come in contact with the electrode 29. Due to the fact that the pressures in the two chambers I4 and I5 were originally equal, this action will occur immediately that the air in the chamber I4 starts to expand and increase the pressure therein. The air in the chamber- I4 will obviously remain expanded as long as the radiant heat is being absorbed by the foil I6 but the increase in pressure in the chamber M will cause some of this gas to pass through the restricted opening 33 so that after a comparatively short time the pressures in the two chambers I4 and I5 will again be equal, and the mercury will return to the position shown in Figures 1 and 2. The device will again be in equilibrium so that as soon as the amount of radiant heat passing through the cup II decreases due to a disappearance of the flame at the oil burner the gas in the chamber I4 will begin to contract resulting in a lower pressure in cham-' This will immediately cause the mercury to rise in the leg 34 and go down in the leg 35 with the result that the mercury will now uncover the electrode 28. Again after a short period of time the pressures in the two chambers I4- and I5 will equalize through the restricted opening 33 and the device will return to a balanced condition.

-It will be seen that this device possesses several advantages, particularly if used for detecting the presence or absence of combustion in an oil or gas burning furnace. In the first place it is compensated for variations in ambient temperature because regardless of the temperature obtaining in the two chambers I4 and I5 their pressures will equalize through the restricted opening 33.

Moreover, due to the fact that the device is norheat passing through the duct II because the.

slow changes will cause correspondingly slow changes in the expansion and contraction of the gas in the chamber I4 and these slow changes in expansion and contraction will be compensated by the leakage of the gas through the restricted opening 33. In other words, this device is responsive to the rate of change of radiant heat passing to the cup II. This device is also not affected by variations in barometric pressure due to the fact that the housing I 0 is completely sealed from the external atmosphere. This also excludes dirt and extraneous matter from the chambers I4 and I5 and thereby prevents clogging of the restricted opening 33.

A' modified form of my invention is illustrated in Figures 3 and 4. This form.of my invention comprises a housing indicated generally at 40,

comprised of a base member 4| and a face 42.

ferentially as indicated at 43 and fits over a com-- plementary shoulder portion on the base 4|. A metal foil 44 similar to the foil |6 shown in Figures 1 and 2 is shown to be of general circular outline and is provided with three projecting cars 45 which are clamped as shown between the base member 4| and the face 42. The base member and face are sealed together in an air tight manner.

The base member 4| is provided with a chamber 45 in which a diaphragm 46, made of some suitable material such as Neoprene, is clamped by means of a plug member 41 shown also as being composed of Lucite. The plug member 41 is provided with a pair of passages 49 connecting the left hand side of the diaphragm with chamber48.

The rear of the base member 4| is provided 4 with a bevelled portion 5| upon which is suitably attached a switch housing 52. is pivotally mounted in the housing 52 as indicated at 54. The free end of the switch arm 53 carries a movable contact 55 which alternately engages the stationary contacts 56 and 51 also mounted in the housing 52. The switch arm 53 also carries an armature 58 adjacent the two poles 58 and 60 of the horse-shoe magnet 6| suitably fastened to the housing 52. It will be obvious that the effect of the magnet 6| upon the armatur 58 is to cause the switch arm 53 to move with a snap action.

This particular construction renders it possible for a single horse-shoe magnet to hold the switch arm 53 into engagement with either the stationary contacts 56 or 51, it being noted that the armature 58 in each case is in the strongest portion of the field of the magnet 6|. This makes it possible to utilize a much smaller magnet than would be the case if the armature 58 were otherwise situated.

The diaphragm 46 is connected, by means of a rod 63 which passes through an "opening 64 in the base member 4| and switch housing 52, to a resilient arm 65 which is in turn connected to the switch arm 53. This resilient connection permits the switch arm 53 to be snapped from one position to theother by means of movement of the diaphragm 46, which seals the chamber 48 from the switch housing 52. Apassage 61 is provided through the base member 4| for affording I restricted communication between the chamber 48 and the external atmosphere within the switch housing 52. A filter 68 is located at the outer end of the passage 6! in order to prevent any dirt from clogging this restricted passage.

It is desired Where this device is used as a combustion responsive device in the control of an automatic fuel burner system that it be easier to actuate the switching mechanism 53 to an elf or safe position than it is to actuate it to its on position. This is so that if there is any tendency of the device to fail, it will fail in a safe position. This result is accomplished in this case by mount ing the switching mechanism at a slightly higher elevation than the diaphragm 46 and the connecting rod 63 is therefore mounted at an angle as shown in Figure 4. It therefore appears that the effect of gravity on all of the moving parts is to tend to move the diaphragm to its collapsed position as shown in this figure. When the switch A switch arm 53 arm 53 is in the position in which the contact 55 is in engagement with the stationary contact 56, the effect Of the pole 58 of magnet 6| upon the armature 58, and also the effect of the diaphragm 46 itself is to resist the movement of the switch arm 53 to the position shown in Figure i. Also if there is any friction at all of the moving parts, and this will include the friction of the connecting rod 63 in the opening 64, this friction will also resist movement of the switch arm 53 to the position shown in the drawing. The angle at which these parts are mounted is so chosen that the elfect of gravity on the moving parts is sufiicient to almost, but not quite, overcome the various fcrces'resisting the movement of the switch arm 53 to the position shown in Figure 4. Thus, a very slight decrease in pressure in the chamber 48 below atmospheric pressure will be sufficient to supply the added force necessary to move the switch arm 53. Therefore the device will be very sensitive to a flame failure at the burner and will very readily move the switch arm 53 to the position shown in Figure 4 to shut down the burner motor.

The operation of this device should now be apparent. When there is no combustion at the burner the pressure within the chamber 48 will be at atmospheric due to the restricted equalizing connection 61. When combustion takes place the radiant heat from the flame will pass through the face 42 of the housing 46 and will be absorbed by the metal foil 44 which will in turn rapidly heat the air in the chamber 48. It will be noted that the sides of this chamber 43 are well rounded. that is there are no sharp corners. As a matter of fact this chamberis in the form of an ellipsoid. By thus shaping the chamber 48, the side walls present a minimum resistance to the flow of convection currents thus providing for a very rapid heating of the air within the chamber. It has been found that the air in this chamber will be heated forty percent faster than if the chamber had square corners such as is illustrated in the device of Figures {1 and 2. The heating of the air in the chamber 48 causes it to expand and increase the pressure therein over the external atmospheric pressure, which will result in the diaphragm 46 being moved towards the right as seen in Figure 4, thus causing the switch arm 53 to move the movable contact 55 into engagement with the stationary contact 56 with a snap action. After a short period of time the pressure in the chamber 48 will return to atmospheric due to the leakage of air through the restricted connection 51. The switch arm 53 will continue to hold the movable contact in engagement with the stationary contact 56, however. Upon the disappearance of flame at the burner, the amount of radiant heat passing through the face 42 will decrease and the pressure within the chamber 48 will immediately decrease below that of the external atmosphere with the result that the diaphragm 46 will move toward the left and the movable contact 55 will again be snapped into engagement with the stationary contact 51.

It will be noted that this device performs the same function as the device illustrated in Figures 1 and 2. This device will also be compensated for changes in ambient temperature due to the fact that the restricted opening 61 will maintain the pressure within the chamber 48 at atmospheric pressure except upon rapid changes in the amount of radiant heat passing through the face 42. This connection also compensates for variaillustrated in Figures 1 and 2.

Figure illustrates a third embodiment of my invention, This figure illustrates a housing indicated generally at which comprises a face member H and two body portions 12 and 73. This housing may be made either of glass as in Figures 1 and 2, or of Lucite as in Figures 3 and 4 or other plastic material. The interior of the housing is divided into two chambers 14 and by means of a diaphragm '16 which seals the chambers in an air-tight manner with respect to each other. The chamber M is provided with a metal foil H which may be of the same shape and mounted in the same manner as the metal foil 44 of Figure 4. There is a restricted connection 18 which connects the two chambers M and 15 for equalizing the pressures therebetween. This restricted connection corresponds to the restricted opening 33 shown in Figures 1 and 2.

The diaphragm is in this case is composed of some resilient material such as phosphor bronze and is slightly larger than the opening in which it is mounted so that upon variations in pressure within the chamber 18 it will snap overcenter from one position to the other. This diaphragm carries at its center a movable contact 19 which in the position shown in the drawing is in engagement with a stationary contact 80 sealed through the housing 10. When the diaphragm I6 snaps to its opposite position this contact 19 is brought into engagement with a second stationary contact 8| which is also sealed into the housing 10.

The operation of this device should now be clear. Upon an increase in the radiant heat passing through the face I l, the heat will be absorbed by the metal foil 11 which will heat the air in the chamber M causing it to expand and snap the diaphragm 16 to the position shown in dotted lines in Figure 5. The pressures in the two chambers 14 and 15 will then be equalized through the connection 18. Upon a decrease in the amount of radiant heat passing through the face I! the temperature of the air in the chamber 14 will decrease and contract with the result that the pressure in this chamber will decrease and the difierence in pressures between the chambers 14 and 15 will then snap the diaphragm 16 back to the position shown in Figure 5.

It will thus be seen that I have designed a device which is extremely sensitive to variations in radiant heat and one which is responsive to rate of change of radiant heat and is compensated for variations in ambient temperature and for changes in barometric pressure.

' As various changes and modifications of this invention will undoubtedly occur to those who are skilled in the art, I wish it to beunderstood that I intend to be limited by the scope of the appended claims rather than by the specific embodiment of the invention disclosed.

I claim as my invention:

1. A radiant heat responsive device comprising in combination a first chamber including a wall capable of passing radiant heat, a second chamber, said chambers being sealed from the external atmosphere, a temperature sensitive fluid in said chambers, means in said first chamber capable of absorbing radiant heat for heating the fluid therein, means responsive to the difference in pressure between said two chambers, control means actuated thereby, and a restricted opening between said two chambers and by-pass- 'ing said pressure responsive means.

2. A radiant heat responsive device comprising in combination a first chamber including a wall capable of passing radiant heat,'a second chamber, said chambers being sealed from the external' atmosphere, a temperature sensitive fluid in said chambers, means within said first chamber capable of absorbing radiant heat for heating the'fluid therein and mounted to permit free circulation of fluid on all sides of said means, pressure responsive means responsive to the difference in pressure between said two chambers, a restricted opening connecting said two chambers and by-passing said pressure responsive means, said pressure responsive means occupying a first position when the pressures in said two chambers are equal, a second position when the pressure in said first chamber is higher due to an increase in the passage of radiantheat through said wall, and a third position when the pressure insaid second chamber is higher due to a decrease in the passage of radiant heat through said wall, and a pair of switches actuated by said pressure responsive means, either one or neither of said switches being closed thereby depending upon which of said three positions said pressure responsive means occupies.

3. A radiant heat responsive device comprising in combination, a substantially cylindrical housing having an end wall capable of passing radiant heat, a partition within said housing separating it into first and second chambers, said first chamber including said end wall, an expansible fluid-in said first chamber, a generally circular sheet of heat absorbing material having a diameter slightly smaller than the internal diameter of said first chamber, means mounting said sheet in said first chamber generally parallel to said end wall and so that said fluid may freely circulate around it, said sheet absorbing radiant heat passing through said end wall and expanding the fluid in said first chamber, means responsive to the difference in pressure between said two chambers, and control means actuated thereby.

4. A radiant heat responsive device comprising in combination, a substantially cylindrical housing having an end wall capable of passing radiant heat, a partition within said housing separating it into first and second chambers, said first chamber including said end wall, an expansible fluid in said first chamber, a generally circular sheet of heat absorbing material having a diameter slightly smaller than the internal diameter of said first chamber, means mounting'said sheet in said first chamber generally parallel to said end wall and at a plurality of spaced points so that said fluid may'freely circulate around it, said sheet absorbing radiant heat passing through said end wall and expanding the fluid in said first chamber, means responsive to the difference in pressure between said two chambers, control means actuated thereby, and restricting means for equalizing the pressures in said two chambers whereby said pressure responsivemeans will respond to the rate of increase or decrease in the amount of radiant heat passing through said end wall.

5. A radiant heat responsive device comprising in combination, a housing having an interior which is sealed from the external atmosphere, a fluid in said housing, a partition dividing the interior of said housing into first and second chambers, said housing having a wall which is capable of transmitting radiant heat, said wall forming a portion of the enclosure for said first chamber, means in said first chamber absorbing the radiant heat passing through said wall for heating the fluid therein, a U tube containing mercury, said tube opening at one end into one of said chambers and at the other end into the other of said chambers, electric contacts extending into said tube, and a restricted opening connecting said chambers independently of said U-tube, said mercury moving in one direction upon an increase in the radiant heat passing through said wall, and in the opposite direction upon a decrease in radiant heat passing through said wall, said movement causing said mercury to cover and uncover at least one of said contacts.

6. A radiant heat responsive device comprising in combination, a housing having an interior which is sealed from the external atmosphere, said housing being filled with a gas having a lower specific heat than air, a partition dividing the interior of said housing into first and second chambers, said housing having a Wall which is capable of transmitting radiant heat, said wall forming a portion of the enclosure for said first chamber, means in said first chamber absorbing the radiant heat passing through said wall for heating the gas therein, a U tube containing mercury, said tube opening at one end into one of said chambers and at the other end into the other of said chambers, electric contacts extending into said tube, and arestricted opening connecting said chambers independently of said U-tube, said mercury moving in one direction upon an increase in the radiant heat passing through said wall, and in the opposite direction upon a decrease in radiant "heat passing through said wall, said movement causing said mercury to cover and uncover at least one of said contacts.

'7. A radiant heat responsive device comprising in combination, a first chamb-enincluding a wall capable of pasisng radiant heat, a second chamber, said chambers being sealed from the external atmospherepa temperature sensitive fluid in said chambers,'means in said first cham= ber capable of absorbing radiant heat for heat- ,ing the fluid therein, means responsive to the difference in pressure between said two chain-= bers, control means actuated thereby, and a restricted opening between said two chambers and by-passing said pressure responsive means, said temperature sensitive fluid being a gas having a lower specific heat than air.

8. A radiant heat responsive device comprising in combination, a housing having an interior which is sealed from the external atmosphere, a fluid in said housing, a partition dividing the interior of said housing into first and second chambers, said housing having a wall which is capable of transmitting radiant heat, said wall forming a portion of the enclosure for said first chamber, means in said first chamber absorbing the radiant heat passing through said wall for heating the fluid therein, a U tube containing mercury,.said tube opening at one end into one of said chambers and at the other end into the other of said chambers, a filter in each end of said mercury tube, electric contacts extending into said tube, and a restricted opening connecting said chambers independently of said U-tube, said mercury moving in one direction upon an increase in the radiant heat passing through said wall, and in the opposite direction upon a decrease in radiant heat passing through said wall, said movement causing said mercury to cover and uncover at least one of said contacts, said fluid being hydrogen gas, said filters preventing the passage of mercury therethrough but permitting the free passage of hydrogen.

9. A radiant heat responsive device comprising in combination, a first chamber including a wall capable of passing radiant heat, a second chamber, said chambers being sealed from the external atmosphere, a temperature sensitive mild in said chambers, means in said first chamber capable of absorbing radiant heat for heating the fluid therein, means separating said two chambers comprising a resilient snap acting diaphragm of the type adapted to remain in either or its actuated positions, said diaphragm being responsive to the difference in pressure between said two chambers, a stationary contact in one of said chambers, movable contact means actuated by said diaphragm, and a restricted connection between said chambers.

10. A radiant heat responsive device comprising in combination a chamber including a wall capable of transmitting radiant heat, said chamber being filled with an expansible fluid, means in said chamber absorbing the radiant heat passing through said wall for heating the air in said chamber, switch means, means for actuating said switch means with a snap action including a diaphragm responsive to the dilierence in pressure inside and outside of said chamber, and a restricted opening associated with said chamber for slowly equalizingthe pressure across said diaphragm following a change in rate of transmission of radiant heat through said wall.

11, A radiant heat responsive device comprising in combination a chamber including a wall capable of transmitting radiant heat, said chamber being filled with a fiuid, means in said chamber absorbing the radiant heat passing through said wall for heating the fluid in said chamber, means including a resilient snap acting diaphragm responsive to the difference in pressure within and without said chamber, a restricted opening for slowly equalizing the pressures across said diaphragm, an increase in the radiant heat passingthrough said Wall causing expansion of the fluid in said chamber and a snapping outwardly of said diaphragm, a de crease in the radiant heat passing through said wall causing a contraction of said fluid and a bowing inwardly of said diaphragm, and control means actuated by said diaphragm.

12. A radiant heat responsive device comprising in combination, a housing forming a chamber, a heat expansible fiuid filling said chamber, said housing having a wall through which radiant heat may pass into said chamber, a sheet of heat absorbent material in said chamber for absorbing the radiant heat passing through said wall and heating the fiuid in said chamber, said sheet being so mounted as to permit free circulation of fluid on all sides of it, said chamber having well rounded sides to facilitate the heating of said fluid by convection upon an increase in the amount of radiant heat passing through said wall, and control means responsive to the pressure in said chamber.

13. A radiant heat responsive device comprising in combination a housing having a base and a face portion forming a chamber-which is substantially in the form of an ellipsoid having a circular center plane, said face portion being capable of transmittingmadiant heat into said chamber, a heat expansible fluid filling said chamber, a heat absorbing member disposed in said chamber substantially along said center plane for absorbing radiant heat passing through said face portion for heating the fluid in. said space, and control means responsive to the pressure in said chamber. g,

14. A radiant heat responsive device comprising in combination'a housing having a base and a face portion forming a chamber which is substantially ellipsoidal in form, said face portion being capable of transmitting radiant heat into said chamber, a heat expansible fluid filling said chamber, a substantially circular sheet of heat absorbing material having a plurality of ears extending outwardly therefrom, said sheet being mounted within said chamber by means of said ears which are clamped between said base and face portion of the housing, the diameter of said sheet being smaller than the major axis of the ellipsoid whereby said fluid may circulate freely around said sheet, and means responsive to the pressure in said chamber.

15. A heat responsive device comprising in combination a housing forming a chamber, said chamber being filled with a heat expansible fluid, means responsive to the pressure in said chamber, movably mounted switching mechanism outside said chamber and means operatively connecting said pressure responsive means and said switching mechanism, said switching mechanism having two positions of operation, means resisting movement of said switching mechanism from each of its two positions of operation, said switching mechanism, connecting .means, and pressure responsive means being mounted on a line which is at such an angle to the horizontal that the eifect of gravity on the elements is almost, but not quite, sufficient toovercome .the efiect' of the resisti means to resist movement of the switching mechanism from one of its positions of operation.

16; A radiant heat responsive device comprising in combination a housing forming a chamber, one portion of said housing being capable of transmitting radiant heat into said chamber, a fluid filling 'said chamber, means in said chamber absorbing radiant heat passing through said portion of said housing for heating the fluid therein, means responsive to the difference in pressure between said chamber and another space, switching mechanism, restricted means connectingsaid chamber and other space, and means operatively connecting said pressure responsive means and said switching mechanism, said switching mechanism having two positions of operation, means resisting movement of said switching mechanism from each of its two positions of operation, said switching mechanism,

sufficient to overcome the efiect of the resisting means to resist movement of the switching mechanism from one of its positions of opera tion.

17, A heat responsive device comprising in combination a housing forming a chamber, said chamber being filled with a heat expansible fluid, means responsive to the pressure in said chamber,

movably mounted switching mechanism outside said chamber, said switching means comprising a horse shoe magnet having a pair of poles, an armature therefor pivotally mounted opposite the open end of said magnet, a switch arm connected to said armature and having two positions of operation, said armature being adjacent the face of one of said poles when said switch arm is in one position of operation and adjacent the face of the other of said poles when said switch arm is in its other position of operation.

18. A switching mechanism for use in combination with a heat responsive device comprisin a horseshoe magnet having a pair of poles, an armature therefor pivotally mounted opposite the open end of said magnet, a switch arm connected to said armature and having two positions of operation, said armature being adjacent the face of one of said poles when said switch arm is in one position of operation and adjacent the face of the other of said poles when said switch arm is in its other position of operation.

19. A radiant heat responsive device comprising in combination, a housing forming a chamber, one wall of saidhousing being capable of transmitting radiant heat into said chamber, said chamber being filled with air, means in said chamber absorbing the radiant heat passing through said wall for expanding the air therein, a restricted opening connecting said chamber with the external atmosphere, filter means preventing dirt from getting into said restricted opening, diaphragm means responsive to the difference betweenthe pressure in said chamber and the pressure of the external atmosphere, switching mechanism locatedout- 'side said chamber said mechanism comprising connecting means, and pressure responsive means being mounted on a line which is at such an angle to the horizontal that the effect of gravity on the elements is almost, but not quite,

a movable switch arm having two positions of operation, means causing said switch arm to move with a snap action, means operatively connecting said diaphragm and switch arm, said switching mechanism being mounted higher than said diaphragm and at such an angle with respect thereto that the effect of gravity on the various parts will almost, but not quite, over-- come the effect of the snap action means, friction of the parts, and force necessary to cause movement of the diaphragm, whereby said switch arm will be actuated when the pressure in said chamber is only very slightly less than 6 the external atmospheric pressure.

SIEGFRIED G. ISSERSTEDT. 

